Bilateral amputees face a unique challenge when they attempt to rise out of a chair. To encourage stability, the amputee must ensure their center of mass passes far enough anterior to the prosthetic knee during active bilateral hip extension. Additionally, they must have enough upper body strength to lift themselves off the chair to initiate knee extension.  Balancing these individual tasks requires a significant amount of energy, balance, and faith that the prosthesis will not bend or buckle. The C-Leg and Compact have a special feature that can be used to maximize stability during this cumbersome task.

Second mode in the C-Leg has two basic settings that include basic flexion dampening and increased dampening with knee angle. The basic flexion dampening is defined as the position of the flexion valve with the knee in full extension. The increased dampening with knee angle is the rate at which the flexion valve closes from the initial starting point during knee flexion.  When the basic flexion dampening is maximized (120) the prosthetic knee flexion valve is fully closed.  No changes of he increased dampening with knee angle can affect the rate of further valve closure if the flexion valve is already closed.

The following exercise should be performed initially inside the parallel bars for safety reasons and prior setting of the basic flexion damping to maximum is necessary in the C-Leg programming software. 

Before standing, C-Leg users will need to change both knees to second mode via the remote control. A progressive flexion lock is now enabled during active knee extension (basic flexion dampening at 120). For less active or new users, the progressive flexion lock provides added stability if they begin to fall backward toward their chair when rising. Unlocking the knee can be accomplished via the remote by changing back to first mode. Once in first mode, the knee will flex with the default stance flexion resistance enabled. As always, plugging in the charger will also reset the knee to first mode when using the C-Leg.

Compact knees delivered after 2006 have a therapy mode accessible in C-Soft 2.0 that enables a similar progressive flexion locking function. Neither therapy mode in the Compact nor second mode in the C-Leg will support normal walking. The C-Leg will be fully locked once the user reaches full extension and the Compact will be fully locked once the user reaches a point seven degrees from full extension while rising from a chair. Unlocking the C-Legs or the Compacts via the remotes will enable the user to ride the default stance flexion resistance back to the chair.